I. Field of the Invention
The present invention concerns reflectors for directing and concentrating energy from signal sources such as acoustic transducers. More particularly, this invention concerns a concave signal reflector that redirects energy from a signal source into a uniform output direction and provides all reflected signals with the same phase shift relative to unreflected signals from the energy source.
II. Description of the Related Art
There are many different types of signal reflectors. Signal reflectors have been designed for light energy (such as headlight beams), electromagnetic energy (such as microwave signals), sound energy (such as sonar signals), and many others. For the present discussion, without any intended limitation, xe2x80x9csignal reflectorsxe2x80x9d may also be referred to as beam reflecting devices, parabolic reflectors, beam focusing elements, or other similar terms. Generally, a signal reflector is used in conjunction with a signal source, and serves to redirect energy from the signal source into an output beam of desired shape, divergence, strength, etc. One simple example of a signal reflector is a parabolic reflector positioned behind a light bulb in a flashlight.
Although many types of known signal reflector can be useful for certain purposes, none of these is completely satisfactory for the application of precisely directing acoustic signals in a confined area. This application often occurs, for example, in the business of QUALCOMM CORPORATION, which is the leading provider of fleet and freight management products through its OMNITRACS(copyright) and TRAILERTRACS(copyright) products and services. QUALCOMM INC. also has numerous other, unrelated businesses.
Broadly, the TRAILERTRACS product monitors various raw statistics concerning the state of freight vehicles, such as semi-tractor trailers. For instance, the TRAILERTRACS product can monitor trailer identification, geographical location, load/cargo status, refrigerator operation, fuel usage, engine properties, brake behavior, transmission activity, safety-related statistics, and other parameters. The TRAILERTRACS product also provides various analytical information, such as notifications or alarms that occur when a trailer is lost, there are too many or too few trailers at one location, there is an unauthorized trailer drop, the wrong trailer is connected to a truck, an unscheduled movement occurs, etc.
It is the load/cargo status sensing feature of TRAILERTRACS that creates a need to precisely direct acoustic signals in a confined area, namely the inside of a cargo trailer. However, as mentioned above, none of the known beam reflectors is completely satisfactory for this application. For instance, some known beam reflectors are too large, possibly interfering with cargo loading/unloading, being vulnerable to damage during loading/unloading, or merely occupying valuable space to the exclusion of cargo. Furthermore, as discovered by the present inventor(s), the beam pattern created by known reflectors is not particularly advantageous for use in acoustic cargo sensing applications. Namely, known acoustic reflectors tend to have a beam pattern with excessive peripheral energy and insufficient focal (central) energy. In the trailer environment, this results in transmission of acoustic signals in unwanted areas, such as the trailer""s roof, floor, etc.
Another problem, first recognized by the present inventor herein, has been that many known reflectors redirect signals without regard for the haphazard introduction of phase shift into the reflected signal output. Namely, rays of the reflected signal incur various delays while they proceed out from the signal source and undergo redirection by the reflector. Consequently, the reflected signals may have varying phases relative to each other and to the unreflected signals. With many conventional signal reflector designs, phase shift is not a significant concern because the wavelength of the transmitted signals is relatively insignificant when compared to the physical dimensions of the reflective surface, or because the source signal is not periodic and the concept of phase shift is not applicable. Therefore, the prior art is unconcerned with the phase shift issue, and therefore does not address it.
Consequently, the known beam reflectors are not completely adequate for acoustic cargo sensing applications due to certain unsolved problems.
Broadly, the present invention concerns a concave reflector that receives some energy emanating from a signal source positioned substantially at the reflector""s vertex. Other energy of the signal source exits the reflector directly without being reflected. The reflector is shaped to reflect all received energy in a predefined output direction, and comprises a shape such as a paraboloid. The shape of this reflector also introduces a designated constant phase shift into all reflected energy relative to unreflected energy from the signal source, regardless of where the received energy is received by the reflector. In addition to this reflector apparatus, other aspects of the invention include a process of manufacturing a signal reflector, a product formed by this manufacturing process, and beam shaping process incorporating these principles.
Unlike microwave and radio frequency signal reflectors, the invention takes the unusual approach of introducing selected phase shift into reflected signals. Such phase shift would not be tolerated, for example, in television or radio signals as it would scramble the ultimate output signal. However, this phase shift is perfect for applications using a repeating input signal.
The invention affords its users with a number of distinct advantages. Chiefly, the invention introduces a selected, uniform phase shift into all reflected signals. When the source signal is periodic, this design minimizes near field interference between the reflected signals, since they all have the same phase shift. Furthermore, if the reflector is. designed to implement a phase shift of zero (any multiple of 360 degrees), reflected and non-reflected signals tend to combine additively in the far field, focusing most of the transmitted energy toward the center of the transmission pattern. Near field in this case is the area inside and in front of the reflector, out to a distance roughly equivalent to D2/xcex, where D is the width dimension of the reflector""s aperture and xcex is the wavelength of the transmitted signal. The far field is consequently defined as any area beyond or outside the near field.
The invention also provides a number of other advantages and benefits, which should be apparent from the following description of the invention.